Turbocharged engines commonly include an exhaust driven turbocharger that increases engine output by increasing airflow to the cylinders. As a result, turbocharged engines provide increased horsepower over equivalently sized naturally aspirated engines.
One turbocharger design includes a variable nozzle turbocharger (VNT). VNT's include variable position vanes that regulate the amount of air delivered through the VNT. The vane position ranges from a fully-open position to a fully-closed position. In the fully-closed position, the VNT delivers a maximum amount of airflow to the engine. In the fully-open position, the VNT delivers a minimum amount of airflow to the engine. The vanes can be positioned between the fully-open and fully-closed positions to provide an intermediate amount of airflow to the engine. A vane actuator adjusts the vane position based on a control signal and a vane position sensor generates a signal indicating the actual vane position for feedback control.
Diagnostics are performed to ensure proper operation of the VNT and the vane position sensor. Traditionally, diagnostic limits are established for the fully-open and fully-closed positions. These diagnostic limits are initially established based on VNT specifications and physical system level measurements using test and development of systems/components. The diagnostic limits may be adjusted through trial and error test methods. As a result, the diagnostic limits typically do not properly account for VNT aging effects, interacting effects of the position sensor with a controller or for manufacturing variation. Further, traditional diagnostics do not include diagnostic limits for the range or span between the fully-open and fully-closed positions.